Been busy in the lab...
Amplitude response and THD+N vs frequency (Pout = 1 W). This with the 6LR8 in triode mode and Edcor CXSE-series OPTs. Note these OPTs are rated for use down to 50 Hz, so I'm pushing them a bit to get to 20 Hz, which shows in the THD curve.
~Tom
Amplitude response and THD+N vs frequency (Pout = 1 W). This with the 6LR8 in triode mode and Edcor CXSE-series OPTs. Note these OPTs are rated for use down to 50 Hz, so I'm pushing them a bit to get to 20 Hz, which shows in the THD curve.
~Tom
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Are you sure that is the CXSE?
CXSE is only available in 25W and rated tdown to 20Hz.
The XSE series is only rated to 70Hz, and the GXSE is rated to 40Hz.
I suspect you are using the GXSE series.
I switched to them from the XSE and chose the 15W transformers over the 10W ones even though I'm putting out less than 5W, after hearing the difference.
Larger transformers produce less distortion at the same lower f3 than smaller ones, with the caviat that making the transformer too large adds distortion to detail at low signal levels as hysterisis losses are worse for larger transformers.
I've not tried the CXSE yet because I believe they may be too large for an under 5W output. One of these days I'll break down and buy a set to find out for sure.
Everything in life is a tradeoff.
Nice amp.
I'm using a CXSE25-8-5K for prototyping. I thought it went to 50 Hz, but the Edcor website says 20 Hz. My bad.
I'm a bit surprised by the relatively high THD at LF. In my 300B amp, I seem to recall cutting the THD at 20 Hz by a factor of 2~3 by switching from the Edcor CXSE25-8-5K to transformers from Electra-Print. Granted, the price also went up by a factor of 3 (or maybe 3~4)...
~Tom
I'm a bit surprised by the relatively high THD at LF. In my 300B amp, I seem to recall cutting the THD at 20 Hz by a factor of 2~3 by switching from the Edcor CXSE25-8-5K to transformers from Electra-Print. Granted, the price also went up by a factor of 3 (or maybe 3~4)...
~Tom
I think I see why.
The Edcor is specified at <1dBu
I'm not sure how that is measured but I think that is about 0.775Vrms
The site I found this on however is referencing 300Ohms, so I'm not really sure what they are specifying.
Can anyone explain this?
I would have expected them to spec it at 1W, or at full power.
The Edcor is specified at <1dBu
I'm not sure how that is measured but I think that is about 0.775Vrms
The site I found this on however is referencing 300Ohms, so I'm not really sure what they are specifying.
Can anyone explain this?
I would have expected them to spec it at 1W, or at full power.
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dBu = dB ref 1 mW in 600 ohm = 0.775 V RMS. That's a standard used in pro audio.
Why Edcor use that standard, I don't know. I would rather they spec it at 1 W out or at the rated power. That does explain the higher THD at LF, though. Technically, I don't think Edcor specifies the THD at full power either. Everything is at <1 dBu. Not a useful spec.
Still... At $80/each the CXSE-series is incredible bang for the buck.
~Tom
Why Edcor use that standard, I don't know. I would rather they spec it at 1 W out or at the rated power. That does explain the higher THD at LF, though. Technically, I don't think Edcor specifies the THD at full power either. Everything is at <1 dBu. Not a useful spec.
Still... At $80/each the CXSE-series is incredible bang for the buck.
~Tom
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What noise?
Multimeter (800 kHz BW) says: 30 uV RMS
Spec an says 60 nV/rt(Hz) floor.
Note that I have done nothing to optimize the placement of the OPTs relative to the PT or supply inductor. My setup is an assembled board on a workbench. No chassis or shielding.
~Tom
Multimeter (800 kHz BW) says: 30 uV RMS
Spec an says 60 nV/rt(Hz) floor.
Note that I have done nothing to optimize the placement of the OPTs relative to the PT or supply inductor. My setup is an assembled board on a workbench. No chassis or shielding.
~Tom
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Hi Tom. Sorry I disappeared for a while there, have been busy moving house.
Thanks for all the updated info you sent me, it's very much appreciated.
The last of the parts finally arrived yesterday. Wow, those James OPTs look great. I'm surprised how heavy they are for their 10 watt rating. I'm still searching for an enclosure, will assemble the amp on a breadboard first. Probably start stuffing the board tonight so I'm sure I'll have some questions for you. Can't wait to hear this thing sing!!
All the best, talk to again soon. Regards, Pete.
Thanks for all the updated info you sent me, it's very much appreciated.
The last of the parts finally arrived yesterday. Wow, those James OPTs look great. I'm surprised how heavy they are for their 10 watt rating. I'm still searching for an enclosure, will assemble the amp on a breadboard first. Probably start stuffing the board tonight so I'm sure I'll have some questions for you. Can't wait to hear this thing sing!!
All the best, talk to again soon. Regards, Pete.
Great news, IT WORKS!! I only had one small hiccup, blew the fuse on initial power up due to having the power trafo primary wired wrong. Sorted that out and it's been making beautiful music all weekend. I tried both resistive & resistive w/bypass bias and ended going back to straight resistive for the extra gain. Only because I'd like to be able to use an iPod for a source sometimes and don't want to use a preamp if I can avoid it. Might try LED bias sometime.
I'm a little bit stunned that these tubes are only $6 each. My early impression is that this amp is very detailed and neutral sounding. The sound is very much like my SSE. It'll probable end up running 40 - 50 hours a week at my workplace so I'll put away a stash of 6lr8's. Can't afford to burn up kt88's running that many hours.
All in all I'm very very happy with this project. Thankyou so much Tom for making it avaliable. I'll try to post a photo once it's in an enclosure.
Best regards, Pete.
I'm a little bit stunned that these tubes are only $6 each. My early impression is that this amp is very detailed and neutral sounding. The sound is very much like my SSE. It'll probable end up running 40 - 50 hours a week at my workplace so I'll put away a stash of 6lr8's. Can't afford to burn up kt88's running that many hours.
All in all I'm very very happy with this project. Thankyou so much Tom for making it avaliable. I'll try to post a photo once it's in an enclosure.
Best regards, Pete.
Awesome! Thank you for sharing.
Yeah... Shorting out the transformer primary is a good way to blow fuses...
I had the same experience. The sweep tubes are really incredible bang for the buck.
You're quite welcome. Thank you for reporting your success building one of these amps using my boards. Please post a picture of the completed amp on this thread once you have it. It's always fun to see the end result.
Yep. I plan to use one for powering my computer speakers and one at work for driving headphones.
50 tubes will keep you going for a while...
The board brings the heater voltage out directly to a terminal block so using the 21 V heater versions is easy as pie.And, actually, the 4 W you get with 6LR8 in triode mode - or 6 W in UL mode - is more than enough for most speakers even when used in a reasonably sized living room. Unless you need 120 dB SPL, of course...
~Tom
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Oh, I see. So you want two output tubes in parallel for more power?
I suppose if you could find a pair of 6LR8 with matched output sections, you could disable the input section of one tube and run the output pentodes in parallel. I haven't tried this. I'll leave it as an exercise for the reader...
~Tom
I suppose if you could find a pair of 6LR8 with matched output sections, you could disable the input section of one tube and run the output pentodes in parallel. I haven't tried this. I'll leave it as an exercise for the reader...
~Tom
Novar spud bulletproof
A quick update on the Novar spud amp I built using the PCB from DIYaudio member tomchr. This sweet little amp has run 40+ hours per week, every week, at my workplace since it was built in October last year. It has been through extremes of temperature(43 deg c+); dust storms; knocked about; and seen several power outages (on/off/on/off/on) during thunderstorms. Twice I have forgotten to turn it off over the weekend, with no ill effects. Apparently, it is bulletproof. Visitors to my workshop often compliment me on the " sweet tunes ". Tom, are these boards still available as I would like to build another one for a very dear friend of mine? Many thanks, and cheers from Central Australia. Pete.
A quick update on the Novar spud amp I built using the PCB from DIYaudio member tomchr. This sweet little amp has run 40+ hours per week, every week, at my workplace since it was built in October last year. It has been through extremes of temperature(43 deg c+); dust storms; knocked about; and seen several power outages (on/off/on/off/on) during thunderstorms. Twice I have forgotten to turn it off over the weekend, with no ill effects. Apparently, it is bulletproof. Visitors to my workshop often compliment me on the " sweet tunes ". Tom, are these boards still available as I would like to build another one for a very dear friend of mine? Many thanks, and cheers from Central Australia. Pete.
Pete,
Good to hear from you. I'm glad to hear that your amp takes a lickin' and keeps on tickin'. I tend to engineer things pretty solidly and it's good to have that confirmed in reality. Thanks for sharing.
I have plenty of boards left. Order as many as you need through my website.
Thanks,
~Tom
Good to hear from you. I'm glad to hear that your amp takes a lickin' and keeps on tickin'. I tend to engineer things pretty solidly and it's good to have that confirmed in reality. Thanks for sharing.
I have plenty of boards left. Order as many as you need through my website.
Thanks,
~Tom
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